首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   420篇
  免费   8篇
  国内免费   2篇
化学   212篇
晶体学   1篇
力学   6篇
数学   65篇
物理学   53篇
无线电   93篇
  2022年   2篇
  2021年   4篇
  2020年   6篇
  2019年   4篇
  2018年   3篇
  2017年   7篇
  2016年   7篇
  2015年   4篇
  2014年   7篇
  2013年   17篇
  2012年   24篇
  2011年   25篇
  2010年   20篇
  2009年   13篇
  2008年   27篇
  2007年   23篇
  2006年   25篇
  2005年   49篇
  2004年   14篇
  2003年   17篇
  2002年   15篇
  2001年   2篇
  2000年   4篇
  1998年   5篇
  1997年   8篇
  1996年   8篇
  1995年   4篇
  1994年   5篇
  1993年   7篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1988年   6篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   2篇
  1982年   6篇
  1981年   6篇
  1980年   3篇
  1979年   3篇
  1978年   3篇
  1977年   3篇
  1976年   3篇
  1973年   3篇
  1970年   2篇
  1968年   2篇
  1965年   1篇
  1961年   1篇
  1943年   1篇
排序方式: 共有430条查询结果,搜索用时 15 毫秒
51.
高效的设计与测试策略需要整个芯片设计和生产生态系统全面努力。 设计和测试部门是否正趋向于融合?在阅读最近一些新闻报道时,您可能会产生这一想法。我曾在一篇早期的评论中提到过设计与测试的关系的问题(参考文献1)。该评论是对此前执行编辑Ron Wilson发表的一篇文章所做的回应(参考文献2)。我坚持自己在今年3月20日发表的文章中得出的结论,即“认为嵌入式仪器会将外置仪器淘汰的想法是错误的”。但是近期的新闻和事件均表明:嵌入式仪器将继续侵入市场。  相似文献   
52.
Summary Gray and Griffeath studied attractive nearest neighbor spin systems on the integers having “all 0's” and “all 1's” as traps. Using the contour method, they established a necessary and sufficient condition for the stability of the “all 1's” equilibrium under small perturbations. In this paper we use a renormalized site construction to give a much simpler proof. Our new approach can be used in many situations as a substitute for the contour method. Partially supported by a grant from the National Science Foundation Partially supported by the Army Research Office through the Mathematical Sciences Institute at Cornell University  相似文献   
53.
The architecture of an optoelectronic recirculating sorter based on the hybrid integration of CMOS logic circuitry, silicon detector/receivers and vertical cavity surface emitting lasers is presented along with the demonstration of the system.  相似文献   
54.
Computer simulations of ice Ih with different proton orientations are presented. Simulations of proton disordered ice are carried out using a Monte Carlo method which samples over proton degree of freedom, allowing for the calculation of the dielectric constant and for the examination of the degree of proton disorder. Simulations are also presented for two proton ordered structures of ice Ih, the ferroelectric Cmc2(1) structure or ice XI and the antiferroelectric Pna2(1) structure. These simulations indicate that a transition to a proton ordered phase occurs at low temperatures (below 80 K). The symmetry of the ordered phase is found to be dependent on the water potential. The stability of the two proton ordered structures is due to a balance of short-ranged interactions which tend to stabilize the Pna2(1) structure and longer-range interactions which stabilize the Cmc2(1) structure.  相似文献   
55.
Ethene reactions with niobium atoms and clusters containing up to 25 constituent atoms have been studied in a fast-flow metal cluster reactor. The clusters react with ethene at about the gas-kinetic collision rate, indicating a barrierless association process as the cluster removal step. Exceptions are Nb8 and Nb10, for which a significantly diminished rate is observed, reflecting some cluster size selectivity. Analysis of the experimental primary product masses indicates dehydrogenation of ethene for all clusters save Nb10, yielding either Nb(n)C2H2 or Nb(n)C2. Over the range Nb-Nb6, the extent of dehydrogenation increases with cluster size, then decreases for larger clusters. For many clusters, secondary and tertiary product masses are also observed, showing varying degrees of dehydrogenation corresponding to net addition of C2H4, C2H2, or C2. With Nb atoms and several small clusters, formal addition of at least six ethene molecules is observed, suggesting a polymerization process may be active. Kinetic analysis of the Nb atom and several Nb(n) cluster reactions with ethene shows that the process is consistent with sequential addition of ethene units at rates corresponding approximately to the gas-kinetic collision frequency for several consecutive reacting ethene molecules. Some variation in the rate of ethene pick up is found, which likely reflects small energy barriers or steric constraints associated with individual mechanistic steps. Density functional calculations of structures of Nb clusters up to Nb(6), and the reaction products Nb(n)C2H2 and Nb(n)C2 (n = 1...6) are presented. Investigation of the thermochemistry for the dehydrogenation of ethene to form molecular hydrogen, for the Nb atom and clusters up to Nb6, demonstrates that the exergonicity of the formation of Nb(n)C2 species increases with cluster size over this range, which supports the proposal that the extent of dehydrogenation is determined primarily by thermodynamic constraints. Analysis of the structural variations present in the cluster species studied shows an increase in C-H bond lengths with cluster size that closely correlates with the increased thermodynamic drive to full dehydrogenation. This correlation strongly suggests that all steps in the reaction are barrierless, and that weakening of the C-H bonds is directly reflected in the thermodynamics of the overall dehydrogenation process. It is also demonstrated that reaction exergonicity in the initial partial dehydrogenation step must be carried through as excess internal energy into the second dehydrogenation step.  相似文献   
56.
Crosslinks are introduced by γ irradiation into 1,2-polybutadiene while strained in uniaxial extension near Tg with stretch ratio λ0, thereby trapping a proportion of the entanglements originally present. The stress at any subsequent strain λ is accurately given by the sum σN + σx, where σN is the stress contributed by a trapped entanglement network with λ = 1 as reference and a Mooney–Rivlin stress-strain relation, and σx is that contributed by a crosslink network with λ = λ0 as reference and neo-Hookean stress-strain relation. The birefringence is accurately given as δn = ?NσN + ?xσx, where the ?'s are the respective stress-optical coefficients. From measurements at λ = λ0 where σx = 0, ?N can be determined separately. For polymer with 88% 1,2 microstructure, ?N and ?x are nearly equal and independent of irradiation dose, though strongly dependent on temperature. For polymer with (95–96)% 1,2, ?N and ?x are different (even opposite in sign) and dependent on dose. This behavior is associated with a side reaction of cyclization by the γ irradiation, which is inhibited by the 1,4 moiety in the polymer with lesser 1,2 content. It is responsible for residual birefringence in the state of ease (λ = λs) where σN = –σx and the stress is zero.  相似文献   
57.
Abstract— An iminum salt of octaethylbenzochlorin with copper in the aromatic ring, CDSI, was tested for its tumoricidal effects on theA–27 N-[4-(5-notro-2-furyl)-2-thiazoly] formamide tumor line. CDSI was found to be an effective photosensitiz4r in vivo when used in combination with either a xenon arc lamp or a pulsed alexandrite laser. Hemodynamically, CDSI and light caused a rapid decrease in tumor blood flow. skin photosensitization was found to be minimal when drug-injected mice werwe illuminated in a solar simulator.  相似文献   
58.
Rick Nelson 《电子设计技术》2009,(3):60-60,62,64-65
今天,忙碌穿梭的消费者也许觉得随身携带的不过是一台手机,而实际上,他们正带着七个以上射频,用于处理多频段蜂窝工作、Wi—Fi网络、蓝牙连接、辅助GPS(全球定位系统)等等功能。今后,他们还会拥有实现Adhoc式设备间通信的射频,  相似文献   
59.
Team sport competition can be characterized as a complex adaptive system in which concepts from nonlinear dynamics can provide a sound theoretical framework to understand emergent behavior such as movement coordination and decision making in game play. Nonlinear Pedagogy is presented as a methodology for games teaching, capturing how phenomena such as movement variability, self-organization, emergent decision making, and symmetry-breaking occur as a consequence of interactions between agent-agent and agent-environment constraints. Empirical data from studies of basketball free-throw shooting and dribbling are used as task vehicles to exemplify how nonlinear phenomena characterize game play in sport. In this paper we survey the implications of these data for Nonlinear Pedagogy, focusing particularly on the manipulation of constraints in team game settings. The data and theoretical modeling presented in this paper provide a rationale in nonlinear dynamics for the efficacy of a prominent model of game play teaching, Teaching Games for Understanding approach.  相似文献   
60.
手机市场有巨大的潜力。高通公司首席运营官兼高通CDMA技术总裁sanjay K Jha在今年6月11日的设计自动化研讨会的主题演讲中称,今天的无线用户有20亿,而到2020年,将有90亿人成为潜在的客户(摩托罗拉后来雇用Jha为协作首席执行官)。Jha也指出了这个爆炸性市场的一个缺陷:90亿潜在用户中,很多人在手机上的花费不超过15美元或20美元。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号